Streamflow and hydrograph learning objectives 1.Learn where to find electronic hydrology data and download it 2.Learn how to interpret hydrographs 3.Understand flood frequency terms and methods including binomial risk assessment 4.Understand watershed terminology 5. Learn how to use Manning’s equation and understand variables that go into it 6.Understand the continuity equation for streamflow 7.Learn how to measure velocity and compute discharge

RUNOFF Component of hydrologic cycle 3 generally acknowledge methods of generation of runoff –Hortonian overland flow (surface runoff) –Shallow subsurface runoff –Saturated overland flow (return flow)

Types of Runoff Generation Ground water i > f Hortonian Overland Flow Ground water Saturated soil Saturated overland flow

Shallow subsurface flow Sandy loam Clay loam Ground water

Partial Area Runoff Sandy loam Ground water

10 m February 2003 July 2003 August 2003September 2003 Figure 7. Schematic of lateral contraction of surface water expression observed around channel heads in stream at RotTags.

What is a watershed? The land area that drains into a selected stream or water body Can by very small or very large Called catchments in the rest of the world Usually based on surface topography- subsurface features may not mimic surface ones as far as drainage is concerned

Watershed areas Area is a basic piece of information that one needs for many purposes, e.g., –Trees /area –Runoff / area –Soil nutrients / area –Watershed area defines the area that delivers water, sediment and nutrients to a water body

Graphic method of measuring area Count the vertices within the area Each vertix represents the center of the area around it Scale 51 vertices

Graphic method for area Trace your watershed on vellum or other transparent paper Lay the area over gridded graph paper Count the number of vertices Use the scale on your map to figure out how much area one square of your graph paper represents Multiple the area of one square by the number of vertices you counted

Who measures water and watersheds? USGS- US Geological Survey USBoR – US Bureau of Reclamation USACOE – US Army Corp of Engineers USFS – US Forest Service NRCS – National Resources Conservation Service USEPA – US Environmental Protection Agency USFWS – US Fish and Wildlife Service NOAA – National Oceanic and Atmospheric Administration NMFS – National Marine Fisheries Service TRIBES Cities, counties, states, schools

Watershed data –EPA Surf your watershed Climate data (national and international) Washington Examples of where to locate national data for watersheds and streams

Stream data- quantity and quality –USGS Water Resources Data Soils data – Aquatic biologic indicators – Examples of where to locate national data for watersheds and streams

Runoff Precipitation Topography Basin size Basin shape Soils Geology Land cover/land use Aspect Factors affecting runoff

Factors Affecting Runoff Precipitation- –Type –Duration –Amount –Intensity –Design storm event –Direction of movement –Extent

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed Shape of watershed Aspect of watershed Geology Soil Land cover

Effect of watershed area 1mm of rain on 1km 2 of watershed represents an input of 1,000 m 3 of water or about 250,000 gallons of water. If you prefer, 1inch of water on a 1mile 2 watershed represents an input of 17 million gallons of water. If a watershed, of 11 mile 2 receives an annual precipitation of 40 inches, that is about 7.6 billion gallons of water each year or just over 1 billion ft 3. If just 15% ran off, this would be an average discharge of 4.8 cfs.

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed –May include drainage density effects Shape of watershed Aspect of watershed Geology Soil Land cover

Topography and drainage density Slope affects stream velocity Drainage density affects travel time of precipitation to channel

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed –May include drainage density effects Shape of watershed Aspect of watershed Geology Soil Land cover

Effects of watershed shape on runoff Higher runoff rates More likely to reach outlet at same time Elevated rates may persist longer as runoff from upstream continues to arrive downstream

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed –May include drainage density effects Shape of watershed Aspect of watershed Geology Soil Land cover

Effects of watershed aspect on runoff Aspect is the compass direction that the slope of the watershed faces Often minimized by variety and complexity of aspects throughout watershed Can affect air, water and soil temperature and therefore snowmelt rates and ET rates –And vegetation communities

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed –May include drainage density effects Shape of watershed Aspect of watershed Geology Soil Land cover

Effects of watershed geology and soil on runoff Geology affects depth to bedrock Affects fracture rates and porosity of bedrock Geology affects soil properties such as texture and porosity which affect infiltration rates Geology affects groundwater divides and thus baseflow delivery Antecedent soil moisture level

Watershed Factors that Affect Runoff Size- area of watershed Topography – slope of watershed –May include drainage density effects Shape of watershed Aspect of watershed Geology Soil Land cover

Land cover effects on runoff ?

Hydrographs Hydrographs depict water amount over time Integrate the watershed response to precipitation Units may be –stage (depth of water) in channel –discharge (volumetric rate) –depth of runoff (volume in channel / area of watershed)

Fig. 5.1

Fig. 5.3

Fig. 5.13

Fig. 5.14

Hydrographs Can depict an event Can depict a season or year Can depict longer periods

Hourly data

Daily stream discharge for January 2004

Mercer Creek- Average January Discharge in cfs

Mercer Creek Average Annual Discharge in cfs

Chehalis River- Average monthly discharge (cfs) Water Years

Water year 2004